The present invention relates generally to transmitter architectures, and more particularly, to a transmitter architecture that is capable of accepting variable input rate data and, using a multitude of modulation formats, transmit the data at a constant symbol rate without a priori knowledge of the input rate.
Communication systems are commonly required to transmit data from a number of different sources. Often, the data rates vary among these sources, requiring the transmitter to accommodate a range of input data rates. Variable rate systems can be much more complicated than systems that operate with a single clock rate. A programmable transmit module developed by the assignee of the present invention is a prime example of this. One such programmable transmit module is disclosed in U.S. patent application Ser. No. 08/543,814, filed Nov. 16, 1995 and assigned to the assignee of the present invention. The forward error correction circuit used in the programmable transmit module must operate at all rates, requiring a very complicated clocking scheme. Additionally, switching data rates often requires reconfiguration of the transmitter by way of a command of some sort.
Therefore, it would be desirable to have a transmitter architecture that is more flexible than conventional designs, and which is capable of accepting variable input rate data and, using a multitude of modulation formats, transmit the data at a constant symbol rate without a priori knowledge of the input rate.
The present invention comprises a self-selective multi-rate transmitter, that includes a plurality of single input, multiple output interleavers receive variable rate input data and generate parallel output data streams that are a function of the data rate of the input data, and that correspond to uncoded k-bit symbols of an M-ary signal constellation. The interleavers are coupled to a modulator that processes the uncoded k-bit symbols to generate the M-ary signal constellation that is a function of the number of parallel output data streams generated by the interleavers. An exemplary modulator used in the transmitter includes a forward error correction circuit that generate n parallel channels of coded data, one parallel channel for each bit in the required M-ary signal constellation, a vector modulator, an upconverter, and an amplifier.
The present invention thus provides for an architecture for a self-selective multi-rate transmitter that is capable of accepting variable input rate data and, using a multitude of modulation formats, transmit the data at a constant symbol rate without a priori knowledge of the input rate. The majority of the self-selective multi-rate transmitter operates at a constant clock rate, greatly reducing the complexity of the forward error correction circuitry and other circuits.
The self-selective multi-rate transmitter employs a modulator that automatically selects between a multitude of signal constellations, depending on the rate of the source data to be transmitted. By doing so, the modulator is used to transmit data from various sources, each with an independent data rate. The modulator performs data formatting, forward error correction encoding, modulation onto an intermediate frequency, frequency conversion to a transmit radio frequency, and amplification with automatic gain control.
Each single-input multiple-output interleaver provides a multiple of parallel data channels to the forward error correction circuitry. The data is conveyed over a varying number of the parallel channels. The forward error correction and modulation are arranged such that the proper signal constellation is automatically addressed by the active data channels.
The present transmitter eliminates the need for the proper modulation format to be identified and selected, either through rate detection or commanding of the transmitter. The present transmitter is capable of operating autonomously, providing the proper waveform with no interaction or complex rate detection.